Addition reaction-curing organopolysiloxane compositions cure relatively rapidly at room temperature or when heated, and for this reason have been broadly examined as protectants for metal surfaces. These compositions are composed of an organopolysiloxane that contains at least 2 alkenyl groups in each molecule, an organopolysiloxane that contains at least 2 silicon-bonded hydrogen atoms in each molecule, and a hydrosilylation catalyst.
However, addition reaction-curing organopolysiloxane compositions generally exhibit poor adhesion, and this deficiency has necessitated the addition of an adhesion promoter in order to equip these compositions with self-bondability. A variety of adhesion promoters are known for this purpose. The following have already been disclosed as curable organopolysiloxane compositions with improved self-bonding properties: curable organopolysiloxane compositions that contain acryloxy-functional or methacryloxy-functional organoalkoxysilane (Japanese Patent Publication Number Sho 51-28309, curable organopolysiloxane compositions that contain the reaction product from epoxy-functional alkoxysilane and alkenyl-containing siloxane (Japanese Patent Publication Number Sho 52-48146 and Japanese Laid Open [Kokai or Unexamined] Patent Application Number Hei 1-85224, and adhesion promoter-containing curable organopolysiloxane compositions, for example, as disclosed in Japanese Laid Open Patent Application Number Sho 54-80358, whose adhesion promoter is prepared, for example, by the reaction of aminoalkylalkoxysilane and epoxyalkylalkoxysilane (refer to Japanese Laid Open Patent Application Number Sho 48-75633 or by reacting alkoxysilane with (i) active hydrogen-containing amine compound or aminoalkylalkoxysilane and (ii) epoxy-functional organic compound or epoxyalkylalkoxysilane, with the proviso that at least one of (i) and (ii) is the alkoxysilane (refer to Japanese Laid Open Patent Application Number Sho 61-72077.
When cured at around 150.degree. C., the curable organopolysiloxane compositions disclosed in Japanese Patent Publication Numbers Sho 51-28309 and Sho 52-48146 and Japanese Laid Open Patent Application Number Hei 1-85224 exhibit an excellent adhesiveness for substrates such as iron and aluminum, but exhibit an inadequate adhesiveness for substrates such as nickel-plated substrates and copper. As a result, when these compositions are adhered on the surface of a substrate chosen from the latter group, delamination occurs rather easily when the adherent is treated with an acidic aqueous solution. In the case of the adhesion promoters taught in Japanese Laid Open Patent Application Numbers Sho 48-75633 and Sho 61-72077, foaming occurs when addition reaction-curing organopolysiloxane compositions that contain these adhesion promoters are subjected to heat curing since these adhesion promoters are extremely unstable because they contain both hydroxyl and silicon-bonded alkoxy in the molecule.